Deviated conductor driving system

ABSTRACT

A method and technique for a deviated (non-vertical) emplacement of a conductor casing at a desired .[.curver.]. .Iadd.curve .Iaddend.and orientation in order to facilitate directional drilling of a well in the substratum of an offshore well site. The method provides for the installation of a relatively short, offset portion of the conductor casing at only the bottom of the conductor pipe string and thereby utilizing this offset portion to force the conductor string in a desired direction and orientation by driving or forcing the conductor casing through a substratum in such a manner that the casing will assume the desired curvature and direction as it advances through the substratum. In addition to the offset or dog-leg segment at the bottom, key-way type guide bars can be added in the longitudinal direction to resist undesired rotation of the conductor pipe.

BACKGROUND OF THE INVENTION

1. Field of Invention

The present invention relates to a system (method and structuralaspects) for emplacement of a conductor casing at a desired curve andorientation from an offshore platform in order to facilitate directionaldrilling of a well in the substratum of an offshore well site.

2. Prior Art

The reasons for directional drilling of a hydrocarbon producing well arewell known. For instance, in connection with offshore production, it isthe usual practice to place a stationary platform in a desired locationfor the optimum production of substrata hydrocarbons. From thisstationary platform a number of wells are drilled.

Obviously, because of the size and location of the hydrocarbon deposits,it is necessary to penetrate the substrata at various locationsaccording to the geological formations available for production. Inorder to obtain maximum production from a given platform with a numberof well locations, it is necessary to drill into the substrata atvarious predetermined depths and orientations.

However, the initial step in the drilling process includes theinstallation of a surface casing which is normally, a steel pipe ofrelatively large diameter. In the case of offshore drilling this surfacecasing is commonly called the "conductor pipe". This portion of thecasing system through which the well is drilled provides the "hole inthe water" through which the remaining smaller casing and the drillstring can be installed. The primary function of this conductor pipe isto provide the hole in the water as mentioned as well as a seal belowthe mudline to a predetermined depth according to the requirements ofthe soil conditions encountered.

Normally, the conductor pipe is installed to a depth of from 100 to 300feet below the mudline or sea bottom. After the installation of theconductor pipe the remaining smaller casings are placed through thispipe of the desired depth and the well is drilled by means of a drillstring through the series of casings.

In order to achieve a specific direction or orientation of the drillstring, a number of techniques have been developed for diverting ororienting the drill string. In the usual pipe conductor, the conductoris installed in a more or less true vertical position due to thestandard techniques of installation of such conductors. All directionaldrilling or deviated work is done below the bottom of the pipeconductor.

However, it has recently been determined that there are certainadvantages to orienting the conductor pipe in a given direction by meansof curving or bending the conductor below the mudline in such a manneras to orient the drilling operation towards a given target location asit leaves the end of the pipe conductor. By this means a number ofadvantages are gained. It is possible to reach shallower hydrocarbonformations than can be reached by diverting the drilling operation afterleaving a straight vertical conductor. Greater dispersion of drillingoperations can be achieved from a central single platform location. Thismethod can also be used to avoid conflicts with previously installedconductors or operating wells on an existing platform.

In order to achieve the deviation or curvature of pipe conductors thereexist three basic patents involving methods different from the novelmethod included herein. U.S. Pat. No. 3,670,507 (issued June 20, 1972 toMott & Ziober, assigned to Texaco Inc.) as well as U.S. Pat. No.3,687,204 (issued Aug. 29, 1972 to Marshall, et al, assigned to ShellOil Co.) both depend upon the use of a series of offset staggered guidesin the platform structures -- spaced so as to either accommodate acontinuously precurved conductor pipe or force a conductor pipe into acurved form by means of these guides.

In addition, there exists U.S. Pat. No. 3,610,340 (issued Oct. 5, 1971to Ziober, assigned to Texaco Inc.) which contemplates the bending ordeviation of the pipe conductor by forcing it into a predrilled hole ina very hard, consolidated stratum of soil. This latter method hasobvious limitations to a specific type of soil. Also, it involves thenecessity for predrilling in every case.

The first two methods mentioned involving the use of a series of guidesrequire that the platform be specifically designed for curved conductorsat the design stage. That is, a platform which has been built for thenormal vertical conductor installation with vertically aligned guidescannot utilize either of these methods. Thus, because of thepre-curvature of the pipe, there are limited possibilities fordeviations from the predetermined curvature in the field.

For other general, prior art background information, reference is alsohad to U.S. Pat. No. 3,451,493 (issued June 24, 1969 to Storm) as atypical example of what is known in the art as "slant drilling" whereinthe entire drilling derrick is tilted to produce directional drilling.Other general interest prior art patents are U.S. Pat. Nos. 3,610,346(issued Oct. 5, 1971 to Ziober, assigned to Texaco Inc.) and 3,685,300(issued Aug. 22, 1972 to Mott, assigned to Texaco Inc.), the formerusing pre-drilled or pre-formed guide passages in the substratum and abackward drag shoe section (element 26) at the end of the casing, whilethe latter uses the basic support legs of the platform which have beenpre-curved as guides for directional drilling.

General reference is also had to U.S. Pat. No. 3,598,190 (issued Feb. 3,1970 to Pfau, assigned to Shell Oil Co.) which uses deviated drilling inan offshore "Salt Dome Drilling Method" and indicates that the course ofthe drilling string may be deflected through a formation by use of anyof the well known devices for this purpose, such as jetting, whipstocksor knuckle joints. As typical examples of directional drilling byjetting or whipstocking, the following U.S. patents are noted:

    ______________________________________                                        Pat. No.      Inventors      Issue Date                                       ______________________________________                                        1,900,163     D. Dana, et al 3-7-33                                           2,420,447     C. H. Schadel  5-13-47                                          2,873,092     R. P. Dwyer    2-10-59                                          2,953,350     S. C. Moore    9-20-60                                          3,000,440     R. H. Malcomb  9-19-61                                          3,593,810     Roger Q. Fields                                                                              7-30-71                                          ______________________________________                                    

Other general interest references in the field of directional drillingin an offshore environment are noted below:

    ______________________________________                                        Pat. No.     Inventors       Issue Date                                       ______________________________________                                        2,565,794    G. L. Young     8-28-51                                          3,004,612    D. C. Kofahl    10-17-61                                         3,390,531    L. P. Johnston, et al                                                                         7-2-68                                           3,542,125    Philip S. Sizer 11-24-70                                         ______________________________________                                    

GENERAL DISCUSSION OF INVENTION

The present invention is applicable to the placement of deviatedconductors from an offshore platform, particularly where there isincluded on the platform a series of standard conductor guides which arevertically aligned, that is, their openings define a straight line in atleast a generally vertical direction.

The preferred method of the present invention comprises the method ofdiverting a conductor by means of welding a short section of the pipe onthe bottom of the conductor at a slight angle to the vertical axis ofthe conductor. Before the vertical staright conductor pipe is insertedin the vertically aligned guides, a short section is cut off andre-welded at a slight angle to the axis of the straight pipe, thuscreating what is commonly known as a "dog-leg".

It has been found by experience that this dog-leg is sufficient todivert the conductor in a given direction as the conductor pipe isforced through the substratum soils by means of a pile-driving hammer.The present invention contemplates the installation of the dog-leg, asnoted, on the first incremental length only before installation of thepipe conductor through the vertically aligned platform guides, theconductor being otherwise straight.

The orientation of the dog-leg with respect to a given target directionis maintained by means of painting a longitudinal line on eachincremental segment of the conductor pipe as it is added on. Thus, whenthe dog-leg bottom of the conductor pipe reaches the mudline, thedirection in which this dog-leg is pointing is predetermined. At thispoint normal driving operations can commence.

It has been found that the dog-leg will cause the conductor pipe to bediverted in the direction of its orientation. Depending upon the type ofsoil encountered and based on experience and the amount of dog-leg oroffset, the conductor pipe will be found to assume a smooth curved shapewhich permits the easy installation of smaller casings and eventuallythe drill string required for final completion of the well.

BRIEF DESCRIPTION OF THE DRAWINGS

For a further understanding of the nature and objects of the presentinvention, reference should be had to the following detaileddescription, taken in conjunction with the accompanying drawings, inwhich like parts are given like reference numerals and wherein:

FIG. 1 is a side generalized view of a platform with the preferredembodiment of the conductor of the present invention inserted throughthe vertical guides, with its dog-leg tip just beginning to penetratethe substrata and the curved course it will take shown in phantom line.

FIG. 2 is a "flow chart" type diagram of the preferred embodiment of themethod of the present invention.

FIG. 3 is a partial, side, vertical cross-sectional view taken down thecenter-line of the preferred embodiment of the conductor of the presentinvention, showing the added dog-leg portion at its tip.

FIG. 4 is a horizontal, cross-sectional view of the conductor takenalong section lines 4--4 of FIG. 3.

FIG. 5 is a generalized schematic diagram showing the deviating forcesthat are utilized in the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the present invention is applicable to theplacement of deviated conductors from an offshore platform, particularlywhere there is included on the platform a series of standard conductorguides which are vertically aligned, and hence the preferred embodimentwill be discussed with respect thereto. However it should be understoodthat some of the benefits of the present invention can be realized evenwhen the guides are not vertically aligned.

Referring to FIG. 1, a platform structure 10 is illustrated in thenormal partially submerged position at an offshore body of water for thepurpose of drilling exploratory gas or oil wells. To fully explore thesubstratum, diverse wells are normally drilled to assume one or moredirections radially outward from the platform 10. The marine platformcomprises in essence a deck 11 which is supported above the water'ssurface by downwardly extending legs 12. The illustrated platform lacksuniqueness in itself, being in general of a well known design for astable vehicle used to drill such offshore wells.

While only two support legs such as 12 are shown, it should beappreciated that this is merely an illustrative embodiment into whichthe invention is incorporated. The respective legs may constitute anyreasonable number depending on the condition of the substrate, the depthof the water and other design and engineering factors.

To provide platform 10 with stability regardless of water turbulence andweather at the offshore location, a series of vertically spacedcross-braces 12' extend between, and are rigidly connected to therespective legs. The number and size of such braces is dependent uponthe depth of the water in which the platform is used as well as on otherdesign considerations.

At the platform top side, deck 11 supports a drilling rig 16 whichembodies in essence a derrick adapted to raise or lower and suspend adrill string, draw works, and rotary table. One or more cranes (notillustrated) are spaced about the deck to handle materials and transferequipment to and from boats. The rotary table provides a means for thedrill string to be controllably rotated for insertion into the well. Inthe normal manner, the derrick is disposed in a generally verticaldisposition. Further, said derrick as well as the draw works is somounted as to be horizontally movable about the deck's surface to allowproper orientation over a particular deck opening.

The mobility of the rig units along deck 11 is necessitated to permitalignment over any of the widespread conductors for drilling in diversedirections.

Platform 10 is provided with conductor guide means 13a-13D adapted toreceive a downwardly moving, normally straight conductor and to guidethe latter vertically down to the mudline 20. Each conductor guide means13 typically comprises a cylindrical section 14 with a flared top 15.

Conductors are normally formed of an elongated cylindrical memberapproximately 16 to 36 inches in diameter, fabricated of steel pipe ortubing, normally made up in short incremental lengths varying from fortyto sixty feet. Again, following normal practice, conductor pipe 1 islowered into place from deck 11 until the lower end is disposed adjacentthe ocean floor 20. The conductor pipe is progressively elongated bywelding incremental sections to the upper end as said conductor islowered.

As best seen in FIG. 3, a conductor pipe, modified in accordance withthe present invention, includes a short dog-leg section 1a welded withan offset from the vertical of angle σ to the balance of the initialconductor segment 1b by means of weldments 4. The dog-leg section can betypically 8 feet in length (longer or shorter as may be indicated orrequired) with a typical offset of approximately one-half inch. Thisoffset may vary from 1/2 inch to the total clearance allowed by theguides 13.

The amount of this offset is a function of several factors. The limitingfactor which governs the maximum offset is the amount of clearancebetween the outer circumference of the conductor pipe when placedvertically through the guides 13 and the inner surface of the platformguides 13. Normally this clearance is approximately 2 inches. It hasbeen found that an offset of approximately one-half inch is sufficientfor most soils. However, this can be increased according to therequirements of the particular soils encountered. Additional offset canbe obtained by reducing the diameter of the conductor, thus allowing forgreater guide clearance which permits greater offset.

If desired and as illustrated, a standard drive shoe 2 also can beprovided at the distal end of the conductor 1.

In addition to the welding of the short dog-leg segment 1a at the bottomof the conductor, it is also possible to prevent or minimize anytendencies of the pipe to rotate by means of welding at least onecontinuous flat bar 3 of steel along the exterior of this dog-legsegment 1a parallel to the axis of the pipe, as illustrated in FIGS. 3and 4. It is noted that the location of additional guide bars aresuggested in FIG. 4 by means of the phantom lined elements 3'. The sizeof this flat bar 3 is limited by the guide clearance available. In wellconsolidated substrata soils the flat bar or bars will act to form a"key-way" which will prevent the end of the pipe 1 from rotating in anundesirable direction. In addition, this guide bar 3 may be extendedpast the welded connection 4 between dog-leg segment 1a and the straightpipe 1b so as to provide additional reinforcing for this welded joint(note phantom line guide bar extension 3a in FIG. 3).

As generally illustrated in FIG. 2, the preferred method of the presentinvention thus comprises the method of diverting a conductor by means ofwelding a short section of the pipe on the bottom of the conductor at aslight angle σ to a vertical axis of the conductor. Before the verticalstraight conductor pipe is inserted in the vertically aligned guides13a- d, a short section 1a is cut off and re-welded at a slight angle σto the axis of the straight pipe, thus creating what is commonly knownas a dog-leg.

It has been found by experience that this dog-leg 1a is sufficient todivert the conductor 1 in a given direction from the vertical 23 as theconductor pipe 1 is forced through the substratum soils 21 by means of apiledriving hammer to produce a total angular deviation Δ whichprogressively gets greater. The present invention contemplates theinstallation of the dog-leg 1a, as noted, on the first incrementallength only before installation of the total pipe conductor 1 throughthe vertically aligned platform guides 13, the conductor 1 though beingotherwise straight.

The orientation of the dog-leg 1a with respect to a given targetdirection is maintained by means of painting a vertical line on eachincremental segment of the conductor pipe 1 as it is added on. Theinitial painted line is preferably put on and in line with the same sideof the pipe where the dog-leg 1a is pointing and thereafter a paintedline is added at each joint matched with the stripe of the precedingjoint. Thus, when the dog-leg bottom 1a of the conductor pipe 1 reachesthe mudline 20, the direction in which this dog-leg 1a is pointing ispredetermined. At this point normal driving operations can commence.

It has been found that the dog-leg will cause the conductor pipe 1 to bediverted in the direction of its orientation. Depending upon the type ofsoil encountered and based on experience and the amount of dog-leg oroffset, the conductor pipe 1 will be found to assume a smooth curvedshape (note phantom line element 22 of FIG. 1) which permits the easyinstallation of smaller casings and eventually the drill string requiredfor final completion of the well.

As generally illustrated in FIG. 5, the forces which cause the desireddeviation are a combination of the driving force down conductor 1 beingmet by the strata resistance acting on the angular or offset dog-legsegment 1a to produce a resulting direction of deviation.

If excessive curvature should occur due to formation encountered, thereis available a method for controlling this excessive curvature. Bydrilling out through the casing 1 at periodic intervals, a survey of theamount of curvature can be obtained in accordance with standardprocedures. If the survey indicates excessive curvature, the stratum ofsoil below the conductor pipe 1 can be drilled out with an under-reamertype drill or other means for a short distance beyond the end of theconductor 1. This creates a large hole or cavity and it will be foundthat the end of the conductor pipe 1 will then tend to drop down in sucha manner as to decrease the curvature in accordance with the targetdirection requirements.

If a greater curvature is required, a slight increase in the originaldog-leg offset σ will cause a greater or sharper curvature radius. Theamount of the dog-leg 1a, as noted hereinabove, is based on a study ofthe soil data as well as field experience with various soilsencountered. In addition, some control can be achieved by varying theamount of energy applied to the pipe by means of the pile-drivinghammer.

Because many varying and different embodiments may be made within thescope of the inventive concept herein taught, and because manymodifications may be made in the embodiment herein detailed inaccordance with the descriptive requirements of the law, it is to beunderstood that the details herein are to be interpreted as illustrativeand not in a limiting sense.

What is claimed as the invention is:
 1. A method providing a deviatedconductor system at an offshore body of water site for directionaldrilling of wells comprising the following steps:a. providing an openended conductor casing of incremental segments; b. securing an openended dog-leg section on the distal end of the otherwise straightconductor producing a longitudinally elongated, off-set portionextending over laterally past one side of the outer circumference of theotherwise straight conductor, said off-set being open ended; c..[.setting.]. .Iadd.lowering .Iaddend.said conductor .[.throughvertically aligned guides.]. .Iadd.down .Iaddend.until the muoline isreached, maintaining or positioning the dog-leg in the desireddirectional orientation; and d. driving said open ended conductor withsaid open ended dog-leg section through the substratum causing theconductor to be laterally deviated due to the interaction of thesubstratum against the offset, lower side surfaces of said dog-legsection from its entry into the substratum to its final deviatedposition.
 2. The method of claim 1 wherein said method further includesthe step of:e. verifying the curvature and orientation of the deviatedconductor and taking any correctional steps desired to alter thedeviation.
 3. The method of claim 1 wherein step b said dog-leg isprovided by cutting off the tip of the initial conductor segment andrewelding the tip at a slight angle to the axis of the remainingstraight conductor.
 4. The method of claim 1 where there is furtherincluded in the initial steps the step of:adding at least one projectingflat bar along the exterior of the conductor parallel to the mainlongitudinal axis of the conductor to minimize or counteract anytendency of the conductor to rotate.
 5. The method of claim 1 wherein instep b there is further included the step of continuously marking oneach incremental segment of the conductor pipe the directionalorientation of the dog-leg.
 6. The method of claim 5 wherein in step bthe directional position of the dog-leg is recorded by painting alongitudinal line on each incremental segment of the conductor as it isadded onto the preceding ones.
 7. A deviated conductor system for ananchored marine structure at an offshore body of water site adapted fordirectional drilling of wells which comprises:conductor .[.guide.]..Iadd.receiving .Iaddend.means carried on said structure being adaptedto receive .[.and guide.]. a conductor passed downwardly therethrough.[., said conductor guide means including discrete guide units spacedvertically apart in at least substantial vertical alignment.]. ; aworking deck positioned above the water's surface; at least oneelongated leg supportably connected to said working deck and extendingdownwardly to the floor of said body of water; and an elongated openended conductor passing downwardly and .[.registered.]. .Iadd.positioned.Iaddend.in .[.said discrete guide means of.]. said conductor.[.guide.]. .Iadd.receiving .Iaddend.means and penetrating substantiallydown into the substratum of said body of water, and deviated laterallyinto the substratum a substantial distance away from the .[.vertical.].line defined by .[.said guide means,.]. the position of said conductorat the level of said working deck and the point of entry of saidconductor into the substratum, said conductor having an open ended,offset dog-leg segment at its distal end offset a slight amount from thelongitudinal axis of said conductor, which open ended, offset dog-legportion extends over laterally past one side of the outer circumferenceof the main body of the conductor.
 8. A conductor for producing adeviated conductor system for an anchored marine structure at anoffshore body of water site adapted for directional drilling of wellswhich comprises:a substantially long, open ended conductor pipe made upof a multiple number of individual conductor pipe segments weldedtogether; and an open ended offset dog-leg segment secured to its distalend which projects out by means of the offset laterally past one side ofthe main conductor pipe, the conductor otherwise being made ofstraight-in-line segments.
 9. A method of providing a deviated conductorsystem at an offshore body of water site for directional drilling ofwells comprising the following steps:a. providing a conductor casing ofincremental segments; b. welding a dog-leg section on the distal end ofthe otherwise straight conductor; c. .[.setting.]. .Iadd.lowering.Iaddend.said conductor .[.through vertically aligned guides.]..Iadd.down .Iaddend.until the mudline is reached, maintaining orpositioning the dog-leg in .Iadd.the .Iaddend.desired directionalorientation; d. driving said conductor with said dog-leg through thesubstratum causing the conductor to be laterally deviated from its entryinto the substratum to its final deviated position; e. verifying thecurvature and orientation of the deviated conductor and taking anycorrectional steps desired to alter the deviation; and f. if step eindicates excessive curvature, there is included the further step ofdrilling out the stratum of soil below the tip of the conductor pipe fora short distance beyond the end of the conductor, causing the conductorpipe to tend to drop down to decrease the curvature.
 10. A method ofproviding a deviated conductor system at an offshore body of water sitefor directional drilling of wells comprising the following steps:a.providing a conductor casing of incremental segments; b. welding adog-leg section on the distal end of the otherwise straight conductor;c. .[.setting.]. .Iadd.lowering .Iaddend.conductor .[.through verticallyaligned guides.]. .Iadd.down .Iaddend.until the mudline is reached,maintaining or positioning the dog-leg in the desired directionalorientation; d. driving said conductor with said dog-leg through thesubstratum causing the conductor to be laterally deviated from its entryinto the substratum to its final deviated position; e. verifying thecurvature and orientation of the deviated conductor and taking anycorrectional steps desired to alter the deviation; and f. if step "e"indicates insufficient curvature, there is further included the step ofproviding a dog-leg on subsequent .[.conductors.]. .Iadd.conductorsegments .Iaddend.having a greater off-set than originally anticipated..Iadd.
 11. The method of claims 1, 9 or 10 wherein there is included aset of vertically aligned guides and step "c" includes the step ofsetting said conductor through the vertically aligned guides..Iaddend..Iadd.
 12. The system of claim 7 wherein said conductorreceiving means also comprise conductor guide means for guiding aconductor passed downwardly therethrough, said conductor guide meansincluding discrete guide units spaced vertically apart in at leastsubstantial vertical alignment, said conductor also being registered insaid discrete guide means and being deviated laterally into thesubstratum a substantial distance away from the vertical line defined bysaid guide means.